Design And Application Of Potential-electric Field Coupled ESIP System

Electrochemically switched ion exchange(ESIX), via reversible electrochemical modulation of the matrix charge density, is considered an attractive approach due to its selectivity, ecologically benign characteristics and economical advantage. However, the uptake and release of the cations are generally performed separately for the traditional ESIX process with intermittent operation.To realize the effective continues electrochemically switched separation of special aim ions, we have proposed the conception of electrochemically switched ion permselectivity membrane(ESIPM), and the effect of five electrochemically switched ion transport systems with different operation circuits on the cation transport amounts and their transport mechanisms were analyzed deeply based on the PPy/PSS ESIPM with the stainless steel wire mesh(SSWM) conductive substrate.It is found that the potential-electric field coupled ion transport system developed by our group has the highest flux compared with the other four ion transport system and the positive potential differences in the sourcecell and receiving cell have great influence on the flux when the membrane is in the same redox state. Therefore, the effective continuse electrchemically switched separation of different aim ions could be reached based on the potential-electric field coupled ion transport system by developing the different ESIPMs.A potential-electric field coupled ion transport system was used for the ESIP process and the continuous separation of the alkali metal cations based on the PPy/PSS composite membrane. In this system,uptake/release of the target cations can be realized by modulating the redox states of the ESIP membrane, and continuous permselective separation of target cations through it can be achieved by tactfully applying a pulse potential on the membrane and combining with an external electric field. In this paper, the theory calculations about the equivalent circuit of the ion transport system were carried out and used to analyze the cations migration of the ESIP process. It is found that the currents through the source solution and receiving solution can reflect the cations migration in each of the solutions. Influences of the applied cell voltage of external electric field and the pulse(constant) potential across the membrane on the permselectivity of the target K+ were investigated. It is demonstrated that the pulse potential was greatly beneficial for performing the permselectivity of the PPy/PSS membrane for K+, and the potential changes applied on the membrane have great influence on theseparation factor α(K+/Cs+) than α(K+/Li+), but the separation factor α(K+/Li+) is greatly influenced by the cell voltage applied to the ion transport system.Therefore, it is expected that the mechanism study about the ESIP process would provide guidance for operation parameters optimization of the process and materials selection and preparation of the membrane.An in-situ potential-enhanced ion transport system based on the electrochemically switched ion permselectivity(ESIP) membrane was developed for the effective removal of Ca2+ and Mg2+ from dilute aqueous solution. In this system, uptake/release of the target ions can be realized by modulating the redox states of the ESIP membrane, and continuous permselective separation of target ions through an ESIP membrane can be achieved by tactfully applying a pulse potential on the membrane and combining with an external electric field. In this study, Fe HCF-PPy/PSS ESIP membrane with high-conductive and high-flux was prepared using a stainless steel wire mesh(SSWM) as conductive substrate. The driving force for the ion transport was analyzed in details by equivalent circuit in the system. It is found that the FeHCF interlayer between the SSWM substrate and the PPy/PSS layer played an important role in removing Ca2+ and Mg2+ from aqueous solutions, and markedly enhanced the separation performance of the membrane due to the improvement of the interfacial charge transfer as well as the change of surface morphology.Influences of the applied cell voltage of external electric field and thepulse(constant) potential across the membrane on the separation of Ca2+and Mg2+ were investigated. It is demonstrated that the pulse potential was more beneficial for improving the removal efficiency than the constant potential applied on the membrane. The hardness of the treated water was reduced to 50 ppm(CaCO3) by applying a pulse potential of± 2.0 V and an cell voltage of 5.0 V when the initial concentration of Ca2+ was 10 mM(1000 ppm(CaCO3)). It is expected that the in-situ potential-enhanced ion transport system based on the Fe HCF-PPy/PSS membrane could be used as a novel water softening technology.ESIP also could release and solve the concentration polarization and membrane fouling occuring in traditional membrane separation technology as an novel ion ion processing method, therefore, it has broad application prospect.